Purification and high-pressure charging of gas into containers



July 16, 1963 w. B. MOEN PURIFICATION AND HIGH-PRESSURE CHARGING 4.

OF GAS INTO CONTAINERS 2 Sheets-Sheet 1 Filed Nov. 25, 1959 MUQDOW INVENTOR By WALTER/B. MOE N AGENT July 16, 1963 w. B. MOEN PURIFICATION AND HIGH-PRESSURE CHARGING OF GAS INTO CONTAINERS 2 Sheets-Sheet 2 Filed Nov. 25, 1959 4O 5O DENSITY "POUNDS PE 1? CUB/ C FOOT DENS/TVOF OXYGEN A7 85C FIG. 3

O O O O 3 2 mmwvmli k MQDMMQQQ .7 .8 L IOU/0 VOLUME TO7J4L SKSTEM VOLUME RA T/O OF PRESSURE ATM/NABLE B! E VAPOR/1 T/NG L IOU/D OXYGEN mum/r09 By WALTER. B MOEN We! ff AGENT United States Patent 3,097,918 PURIFICATION AND I-IIGH-PRESSURE CHARGING 0F GAS INTO CONTAINERS Walter B. Moen, Berkeley Heights, N.J., assignor to Air Reduction Company, Incorporated, New York, N.Y.,

a corporation of New York Filed Nov. 25, 1959, Ser. No. 855,424 5 Claims. (Cl. 23-4) This invention relates in general to the filling of containers with gas under high pressure; and more specifically, to methods and apparatus for purifying gas, particularly oxygen, during the highapressure charging process.

The storage of oxygen as a gas under high pressure has recently assumed increased importance for 'various aircraft and missile applications, particularly for use in breathing apparatus. A rather extensive study has shown that storage of oxygen in amounts of five pounds or less can be accomplished more conveniently, and with reduced weight and volume penalties, when the oxygen is in the form of a gas rather than a liquid. Moreover, high=pressure gas storage eliminates the problem of dispensing oxygen from a liquid gas converter under varying conditions of vehicle acceleration and gravity. The use of gas pressures of the order of 7,500 pounds per square inch, which are most convenient for aircraft and missile applications, however, creates certain problems in filling the containers. For example, the tendency of oxygen to support combustion in the presence of hydrocarbon impurities is greatly aggravated and ignition is eased by the opening and shutting of valves in the high-pressure systems, making the use of such pressures of questionable safety under prior art conditions. Moreover, in oxygen used for breathing applications at reduced total pressures in the order of 5 pounds per square inch absolute, the presence of even a few parts per million of an odorou-s hydrocarbon impurity causes great discomfort to the user, and have been reported to be toxic.

Accordingly, the general object of this invention is to provide improved techniques and apparatus for filling gas containers under pressure. More specific objects of the invention as applied to the storage of oxygen under high pressure, are to render the filling and use operations less hazardous and the product less toxic -for breathing purposes.

In accordance with the present invention, these and other objects are accomplished in a closed system in which containers are filled with gas by evaporation of a corresponding liquid and subsequent heating of the gas until a desired pressure is reached. A salient feature of the invention is the inclusion of catalytic means in the closed system, the operation of the catalytic means in purging the gas of certain contaminating impurities being substantially facilitated by the elevated pressure which provides a high degree of contact between the catalyst and the gaseous molecules.

In the specific embodiment which will be described in detail hereinafter by way of illustrating the invention, the process is carried out by introducing a quantity of liquid oxygen into a receptacle constructed to withstand high pressures, which is initially jacketed with a Dewar bottle, or other insulating means. The insulating jacket is subsequently removed and replaced by a heating jacket, whereby the temperature of the receptacle is increased until the liquid evaporates and fills the closed system, including a receiving cylinder attached to the outlet, to a pressure of the order of 7,500 pounds per square inch.

During expansion and pressure rise, the gas in the closed vated pressures, the catalytic action is facilitated, causing the oxygen to readily unite with the impurities which are principally hydrocarbons, :for-ming carbon dioxide and water and other products, all of which are subsequently removed from the high-pressure gas after cooling by drying and absorbing agents, such as anhydrous lithium hydroxide and calcium sulphate.

Particular features of the invention are that it substantially increases the safety with which the oxygen can be stored at high pressure by lessening the chance of combustion and explosion; and further, that its operation renders the stored oxygen free from toxic contaminants.

These and other objects, features, and advantages of the present invention will be apparent to those skilled in the art after study of the detailed description hereinafter of the disclosed embodiment with reference to the attached drawings, in which:

FIG. 1A is a schematic diagram of a typical embodiment of ths h-ighpressure filling and purification system of the present invention at the beginning of its operational cycle;

era-tional cycle, wherein a heating device, such as a mantel, replaces the Dewar insulating vessel utilized in the initial stages of the operation;

FIG. 2 is a graph, expository of the operation of the invention, in which density is plotted against pressure tor oxygen at 35 degrees centigrade; and

FIG. 3 is another graph in which the ratio of the volume of liquid introduced into the closed system to the total volume of the system is plotted against the resultant pressure in atmospheres.

Referring to FIG. 1A for a detailed discussion of the disclosed, illustrative embodiment of the present invention, receptacle 1, alternatively called a condenser, is a hollow, cylindrical steel cup about 11 inches high and 4 /2 inches in diameter, constructed with walls a quarterinch thick. The receptacle 1 is constructed and prooftested to withstand a pressure of 15,000 pounds per square inch. An annular yoke 1a fits over the top of the cylindrical container 1, and holds it suspended in a conventional manner, not shown, by means of bolts which screw into a plate abutting from the enclosing cabinet. The yoke 1a forms a flange about a quarter-inch thick at the upper end of cylindrical container 1, acting as a closure therefor, by underlapping the gas-tight seal through which the outlet pipe 3 passes.

An insulating Dewar bottle 2, which is supported in a conventional manner by a plate abutting from the enclosing cabinet, is cylindrical in form, has an inner diameter several inches larger than the outer diameter of the cylindrical receptacle 1, and is several inches higher. Dewar bottle 2 is disposed to provide a jacket, open at the upper end, but closed at the bottom, which fits over and provides an insulating and refrigerating environment surrounding the cylindrical receptacle 1. The Dewar jacket 2 may be of any of the types well-known in the art for providing a high degree of heat insulation to the enclosed body. Moreover, as indicated in the drawing, provision is made for containing liquid nitrogen in the Dewar vessel 2. surrounding receptacle 1 in order to maintain the receptacle 1 at a uniformly low temperature below the liquefaction point of oxygen, while the liquid oxygen is being introduced into the receptacle 1.

The Dewar vessel 2 is readily removable, since it is only employed during the initial stages of the operating cycle, either while the liquid oxygen is being introduced into the enclosed receptacle '1, or, under an alternative arrangement, while gas introduced into receptacle 1 is condensed to liquid. After the termination of this part of the process, Dewar vessel '2 is replaced by a heating FIG. 1B shows the system at a later point in the opmantel 2', in the manner indicated in FIG. 1B of the drawings. Heating mantel 2 is a cylindrical cup of refractory material, the inner diameter and height of which are each somewhat greater than that of the cylindrical receptacle 1, so that it slips into place enclosing the latter in the same position as the Dewar vessel it replaces. Heating mantel 2 contains a high-resistance electrical heating coil, energized from a conventional power source connected to its terminals, which is designed to bring the cylindrical receptacle 1 up to a temperature of about 70 degrees Fahrenheit within a period of approximately 20 minutes, thereby expediting the evaporation of the liquid in the receptacle 1. These values are not critical, however.

The tubing, valves, and coupling elements throughout the system are designed to withstand pressures within the range of 10,000 to 15,000 pounds per square inch. In the present embodiment, steel tubing is used which has a quarter-inch inner diameter, and a three-eighth inch outer diameter. Corresponding high-pressure valves and coupling members are employed.

The outlet pipe 3 leads through a gas-tight seal set into the top of receptacle 1, and overlapping the supporting yoke 10, to a T-junction 4, connected to one arm of which is outlet 5 which leads, under control of the two-way, through-type valve 6, to the terminal 7. The latter is a fitting suitably engineered to make a gas-tight coupling with container 8, which may under alternative arrangements comprise either a tank of liquid oxygen which is poured or siphoned into the receptacle 1, or a container of oxygen gas, which is condensed to liquid phase after entering the receptacle 1.

A second arm 9 of the T-junction 4 is connected to the angle-fitting 10, one outlet of which leads through shutoff valve 10a to the line-filter 12 and the two-way straightthrough relief valve 13, which terminates in the vent 14-. The line-filter 12 comprises a sintered-steel disk, which functions to remove particles of 5 microns or more in cross-section before they reach and unseat the reliefvalve 13. In the present embodiment, the latter is equipped with a stellite stem and seat, and is designed to withstand pressures of between 10,000 and 15,000 pounds per square inch. Its function is to permit the pressure in the system to be readily reduced by manual operation of the valve, should the pressure exceed a desired limit.

The other outlet of angle-fitting 10 connects pipeline 9 under control of the shut-off valve 11 which leads to the inner catalytic chamber 17 of furnace 15.

Chamber 17 may take the form, for example, of a small, steel cylinder, 8 inches long, having an outer diameter 2 inches, and an inner diameter of one inch. Access is had to the interior of chamber 17 by means of a hexagonal-headed plug which screws into one end. The two ends of the chamber are fitted to screw into the quarterinch outer diameter connecting system, the joints in every case being gas-tight.

Chamber 17 is charged with a catalytic agent, the function of which is to eliminate the trace oxidizable impurities present in the oxygen to be stored. Although the oxygen to be stored is of a commercial grade of purity, it can also be presumed to contain of the order of about 5.50 parts per million of impurities, the origin of which are not fully known, although they are most likely condensed out of the atmosphere. Although their identification is not complete, these impurities are believed to include principally hydrocarbons, and compounds of nitrogen and sulphur. Under the operation of the catalyst, the hydrocarbons are converted to carbon dioxide and water, and compounds of nitrogen and sulphur are oxidized to form acidic gases. All of these products are absorbed at a later point in the system. In the embodiment under description, chamber 17 is charged with one-eighthinch alumina pellets, coated with 0.5 percent platinum, which are replaced periodically as the chamber is used. Although this combination has been found to be optimum 4 for the purposes of the present embodiment, other catalysts which might also be found operative as applied to the reaction of hydrocarbons and compounds of nitrogen and sulphur in an excess of oxygen are pallidium, cupric oxide, and other well-known metal or metallic oxide catalytic agents.

The furnace 15, which is a conventional heavy-duty type, comprises a cylindrical refractory body, with an insulating outer shell, of the order of 2 feet long, and 18 inches in diameter, which is hollowed out in the center to provide a cylindrical chamber about 10 inches long and 2% inches in diameter, which accomodates the inner steel chamber 17. The refractory body is hinged along one side to permit ready access to the enclosed chamber 17. High resistance heating coils are embedded in the refractory body. These are designed to consume 1.4 kilowatts, and to cause the furnace to operate at about 800 degrees Fahrenheit (427 degrees centigrade) when energized by a single-phase, 60 cycle, ll0-volt power source. Although the temperature mentioned is deemed to be optimum for a system utilizing the disclosed catalyst and quantities of gas, operative temperatures for the purposes of the present embodiment have been found to lie within the range of 750 to 850 degrees Fahrenheit (399 to 455 degrees centigrade).

It is believed that at the high temperatures and high pressures, there is greatly increased molecular contact between the impurity gases and the elements of the catalyst, which substantially facilitates the desired chemical combinations, forming carbon dioxide and water, and other gases, such as oxides of nitrogen and sulphur, depending on what impurities are present in the gas under treatment. These products are readily removed by selective drying and absorbing agents at a subsequent step in the process.

The gas under purification passes out of the hot catalytic chamber 17, into a cooling-coil 18, which is of stainless steel, having about 10 turns, each of which is about 4 inc-hes in outer diameter. This is disposed in a water bath. The pipe from the cooling-coil 18 is directly connected through a gas-tight screw connection to one end of the absorption chamber 19, which takes the form of a small steel cylinder, 8 inches long, with an outer diameter of 2 inches, and an inner diameter of 1 inch, similar in form to the catalytic chamber 17. It is opened for servicing by a gas-tight screw-plug at the other end, through which connection is made to the outgoing line. The interior of chamber 19 is charged with drying and absorbing material. For the purpose of the present embodiment, anhydrous lithium hydroxide of porous type, 6 to 14 mesh, and anhydrous calcium sulphate, 8 mesh, which is obtained commercially under the trade name Drierite, have been employed to perform the multiple functions of absorbing the water vapor, carbon dioxide, and such other compounds of nitrogen and sulphur as are formed under the action of the catalyst. These drying and absorbing agents are removed and renewed periodically. It will be apparent that although the foregoing absorbing agents have been named by way of example, other similar absorbing agents are also suitable for the uses of the present invention, such as activated alumina, or a mixture of barium and calcium hydroxides, which is obtained commercially under the trade name Baralyme.

The outlet pipe from the absorbing chamber 19 leads directly through the T -connection 24 and the two-way, straight-through valve 21, to the terminal 23, which is suitably engineered for making gas-tight connection to the cylinder 22 to be filled with gas under pressure. Adjacent valve 21, is a conventional pressure gauge 20 connected to another arm of the three-terminal T-connection 24, the gauge being adapted to measure pressures up to about 15,000 pounds per square inch.

It will be understood that prior to assembly, each of the components of the system is thoroughly cleansed of l impurities in accordance with practices well known in the art. For example, the following routine has been found to be satisfactory for present purposes. Each component is first Washed in soap and water, rinsed in water, and dried. It is next washed in acetone, and rinsed in distilled water. The final washing operation is carried out in mild, trisodium phosphate solution at 70 degrees centigrade, with double rinsing, first in distilled water at 70 degrees centigrade, and then in distilled water at room temperature. The component is then carefully dried and stored in a polyethylene bag until the elements of the system are put together.

After the entire system is assembled, prior to use for filling and purifying purposes, it is flushed out with oxygen at a pressure slightly above one atmosphere. At all times thereafter, in order to keep the system free ifirom impurities, the internal gas pressure in the system is maintained slightly positive with respect to the surrounding environment.

Operation of the System The sequence of operations of the system of FIG. 1A, 1B is as follows.

Step 1: The cylinder 22 to be charged with gas is connected to the terminal 23 in a gas-tight connection, and all valves 6, 11, and 21 are closed. The catalytic furnace is brought up to operating temperature, which is about 800 degrees Fahrenheit in the operation under description.

Step 2: The Dewar flask 2 is jacketed around the highpressure receptacle 1. One of the chambers of the Dewar flask 2 is filled with a low temperature refrigerant, such as liquid air, oxygen, or nitrogen.

Step 3: The receptacle 1 is filled with liquid oxygen of a commercially obtainable grade, having a purity of at least 99.5 percent, and containing not more than about 50 parts per million of moisture and hydrocarbons, and about, say, 0.4 percent argon, and 0.1 percent nitrogen. This step may be accomplished by several diliferent methods, of which the following are examp es:

(a) Cylinder 8, containing gaseous oxygen, is connected to valve 6. The gaseous oxygen is permitted to flow into receptacle 1, where it will condense. Then, when the receptacle 1 is filled to the desired level, the gas flow ceases, a fact which is readily noted aurally.

(b) Alternatively, the liquid oxygen is syphoned into the receptacle 1 by placing a second Dewar vessel containing liquid oxygen, around the terminal 7 in place of the gas-filled cylinder 8. Using either of the methods outlined, the step of filling the receptacle -1 with the requisite amount of liquid oxygen requires approximately twenty minutes.

Step 4: Valve 6 is closed; and valves 11 and 21 are opened. A water bath is simultaneously placed around the cooling-coil 18. Dewar vessel 2 is removed from its position jacketing receptacle 1 in order to permit the liquid oxygen to evaporate. As a desirable, but not a necessary step of the operation, the heating mantel 2 indicated in FIG. 1B is jacketed around receptacle 1 to speed up the evaporation process. In preferred arrangement, this step in the process requires about minutes. If it is desired to further increase the speed of the evaporation process, and to reach a high pressure earlier, the heating mantel 2 may be applied while the valve 11 is still closed. Also, if desired, the valve 21 may be adjusted to partially opened position to create a back pressure such that the system upstream of the valve will reach a relatively high pressure promptly.

Step 5: The pressure increase in the system is followed by noting the reading of the gauge 20. When the desired pressure has been attained, the valve 21 is closed.

. 6 As explained in detail hereinbefore, excess pressure may be relieved by operation of the relief valve 13, which may be set at the desired operating point. Alternatively, the excess pressure may be relieved by opening the valve 6.

In assessing the value of high-pressure oxygen storage for air-borne applications, one is referred to FIG. 2 of the drawings which shows a density versus pressure curve for oxygen at 35 degrees centigrade. From this curve, it is seen that 7,500 pounds per square inch (500 atmospheres) at sea level, the density of the gas is about 3-5 pounds per cubic foot, almost half that of liquid oxygen at the normal boiling point.

FIG. 3 enables one to compute the amount of liquid which must be introduced into the receiving receptacle 1 to attain the desired pressure in the closed system. In FIG. 3, the ratio of the volume of liquid initially injected into the receptacle 1 to the total internal volume of the closed system is plotted against the resultant pressure when the liquid is completely evaporated.

In the embodiment under description, the desired pressure of about 7,200 pounds per square inch is attained byevaporating completely, 72 cubic inches of liquid in a closed system which, excluding the container to be filled, has a total internal volume of 14 cubic inches. If V is taken to be the volume of the cylinder to be tilled, then the ratio of the total volume of liquid to be evaporated to the total internal volume of the closed system is Although a specific embodiment of the invention has been described in detail herein by way of illustrating the present invention, it will be understood that practice of the present invention is not limited or circumscribed by the particular forms or combinations of apparatus shown, or by the particular values of parameters employed. For example, in addition to oxygen, which is utilized in the described embodiment, the system of the present invention is also applicable with virtually no equipment modification to the purification and highpressure charging of air, argon, and nitrogen. In case of the latter two gases, the catalyst would include an oxidizing agent, such as 'cupric oxide.

Numerous other variations of the teachings of the present invention, within the scope of the appended claims, will be apparent to those skilled in the art.

What I claim is:

l. The method of charging oxygen, which contains hydrogen and other impurity compounds, under high pressure into a container which comprises the steps of completely evaporating a quantity of liquid oxygen in a gas-tight system to which said container is connected, wherein the ratio of the volume of said quantity of liquid to the total internal volume of said gas-tight system exceeds about 0.4, submitting the gaseous oxygen at the resultant high pressures and at a temperature Within the range of 750 to 850 degrees Fahrenheit to catalytic action to cause oxygen to combine with said hydrogen and said other impurities to form products including carbon dioxide and water, cooling the said oxygen and said products substantially to room temperature, and submitting said oxygen at said high pressures including said products to absorbing means for selectively absorbing said products from said oxygen before said oxygen is charged into said container.

f T-he method of charging a gas selected from the group consisting of oxygen, air, and the relatively inert atmospheric gases under high pressure into a container, said gas containing impurities including hydrogen and hydrocarbon compounds, which comprises the steps of completely evaporating a quantity of said gas from the liquid state in a gas-tight system to which said container is connected, wherein the ratio of the volume of said quantity of liquefied gas to the total internal volume of said gas-tight system exceeds about 0.4, submitting said gas at the resultant high pressures and at a temperature within the range of 750 to 850 degrees Fahrenheit to catalytic action to cause said impurities to oxidize to form products including carbon dioxide and water, cooling the said gas and said products substantially to room temperature, and submitting said gas at said high pressures including said products to absorbing means for selectively absorbing said products from said gas before said gas is charged into said container.

3. The method of charging air under high pressure into a container, said air containing impurities including hydrogen and hydrocarbon compounds, which method comprises the steps ofcompletely evaporating a quantity of liquid air in a gas-tight system to which said container is connected, wherein the ratio of the volume of said quantity of liquid to the total internal volume of said gas-tight system exceeds about 0.4, submitting the gaseous airat the resultant high pressures and at a temperature Within the range of 750 to 850 degrees Fahrenheit to catalytic action to cause oxygen in said air to combine with said impurities to form products including carbon dioxide and Water, cooling the said air and said products substantially to room temperature, and submitting said air at said high pressure including said products to absorbing means for selectively absorbing said products from said air before said air is charged into said container.

4. The method of charging argon, which contains impurities including hydrogen and hydrocarbon compounds, under high pressure into a container, said method comprising the steps of completely evaporating a quantity of liquid argon in a gas-tight system to which said container is connected, wherein the ratio of the volume of said quantity of liquid argon to the total internal volume of said gas-tight system exceeds about 0.4, submitting said gaseous argon at the resultant high pressures and at a temperature within the range of 750 to 850 degrees Fahrenheit to catalytic action by a catalyst including an oxidizing agent to cause said impurities to oxidize to form products including carbon dioxide and water, cooling said argon and said products substantially to room temperature, and submitting said argon at said high pressures including said products to absorbing means for selectively absorbing said products from said gas before said gas is charged into said container.

5. The method of charging nitrogen, which contains impurities including hydrogen and hydrocarbon compounds, under high pressure into a container, said method comprising the steps of completely evaporating a quantity of liquid nitrogen in a gas-tight system to which said container is connected wherein the ratio of the volume of said quantity of liquid nitrogen to the total internal volume of said gas-tight system exceeds about 0.4, submitting said gaseous nitrogen at the resultant high pressures and at a temperature within the range of 750 to 850 degrees Fahrenheit to catalytic action by a catalyst including an oxidizing agent to cause said impurities to oxidize to form products including carbon dioxide and Water, cooling said nitrogen and said products substantially to room temperature, and submitting said nitrogen at said high pressures including said products to absorbing means for selectively absorbing said products from said gas before said gas is charged into said container.

vol. 53, No. 3, March 1957, pages 1l2M121M.

Sheperd et al. in National Bureau of Standards Journal of Research, vol. 22, January-June 1939, pages 301 to 306 incl. 

2. THE METHOD OF CHANGING A GAS SELECTED FROM THE GROUP CONSISTING OF OXYGEN, AIR, AND THE RELATIVELY INERT ATMOSHPERIC GASES UNDER HIGH PRESSURE INTO A CONTAINER, SAID GAS CONTAINING IMPURITIES INCLUDING HYDROGEN AND HYDROCARBON COMPOUNDS, WHICH COMPRISES THE STEPS OF COMPLETELY EVAPORATING A QUALITY OF SAID GAS FROM THE LIQUID STATE IN A GAS-TIGHT SYSTEM TO WHICH SAID CONTAINER IS CONNECTED, WHEREIN THE RATIO OF THE VOLUME OF SAID QUANTITY OF LIQUEFIED GAS TO THE TOTAL INTERNAL VOLUME OF SAID GAS-TIGHT SYSTEM EXCEEDS ABOUT 0.4, SUBMITTING SAID GAS AT THE RESULTANT HIGH PRESSURE AND AT A TEMPERATURE. 